Yes it does – you will stay connected to IRC even if you shutdown your computer or sign out of IRCCloud.com. This means when you come back, you'll be able to see what happened on IRC whilst you were away.

Session limits imposed by the IRC network you were using. They may need to make special allowances for IRCCloud connections

"Zombie Detection" - on the limited trial, you’ll be disconnected from all networks if you don't visit the IRCCloud website for a couple of hours. If you upgrade your account, we’ll keep you connected forever, regardless.

A bug in IRCCloud that caused your connection to bounce (rare, but more likely during beta).

Your IRCCloud account password is stored as a salted hash (bcrypt, with decent work factor), and so is protected; we can't read or discover it

Your nickserv credentials, server password and on-connect commands are stored symmetrically encrypted using a key unique to your account. We need to temporarily decrypt these when we send them to IRC servers

Create a new server, enter your ZNC hostname & port, then instead of putting the ZNC authentication details in the nickname and password field, enter them as username:password in the Server password field.